1. Field of the Invention
The invention concerns a lighting system for lighting fittings, projectors and enlarging apparatuses, which provides an intensive and uniform illumination of a given area at a given distance. It consists of a light source, an auxiliary mirror and the main mirror. Another part of the system is a raster lens, consisting of a net of individual converging lenses, which direct the light rays coming from the source into the required plane, where they create the light spot.
2. The Prior Art
There exist many lighting systems used above all as automobile headlights. These systems are usually made by a continuous parabolic reflector covered by a cover glass with diverging elements. The light source is a halogen bulb with two filaments; one is for distance light and the other one for lower beam with an internal diaphragm that allows limitation of the lower beam. In order to decrease the reflector's vertical size, the classical paraboloidal reflector was remodelled into the shape of a homofocal reflecting surface in such a way that this reflecting surface was divided into a system of discretely connected paraboloidal segments with the same optimized focal length. The need for another decrease of the headlight's size leads to a production of an ellipticdioptric system. Its reflector has a shape of a rotational or polyelliptic ellipsoid with three axes. In one of its focuses there is the filament of the bulb and in the second one there is a diaphragm. The planoconvex lens, situated in the second focus of the ellipse, directs the output light rays so that they are parallel with the optical axis of the system. This lens also projects the diaphragm into the luminous background of the roadway. This process defines distribution of the subdued beam illumination.
As there is only one filament in the bulb, this system can be used for lower beam only. Therefore one more lighting fitting of a similar or the same construction is necesarry for a distance light. The said lighting fitting has a very small height and it creates lower beam of a good intensity and homogenity with a sharp boundary between light cone and darkness. Another lighting fitting with an increased reach of lower beam illumination has a reflector of the type with a freely formed reflecting surface, which is continuous and closed in such a way that, without the influence of a covering glass, the reflector projects to the required space elementary filament of a single filament bulb. Even without the diaphragm, it makes a boundary between darkness and light. Light output capacity of such a system proportionally increases with the size of the reflector and it allows also using of its lower part, what increases the efficiency. Nevertheless, for a distance light an extra lighting fitting is needed. By the use of the conception with freely formed reflecting surface an improved projective elliptical dioptric system of the lighting fitting is achieved. The original ellipsoid is remodelled into a general surface with a higher amount of light beam in the non-diaphragmed part of the focal plane. The reflector is more open in its upper part and more closed in its lower part. The light ouput of such a system is much higher in comparison with the previous system.
Similar lighting systems can be used for different illuminating purposes, e.g. in the health service, as spotlights used in stomatology. These systems consist of a known type of planary lighting fittings using mostly as light sources a halogen bulb, and a cold reflecting concave mirror. Its reflecting part is arranged as raster mirror, which directs the light spot into the required plane.
The main disadvantage of present automobile lighting systems consists in their low luminous efficiency. Moving vehicles use the light beam, reflected by differently shaped mirrors, and the luminous flux coming out of light source straight ahead is not used and is therefore often shaded. Dazzling effect is another big disadvantage of such a lighting fittings, since almost all systems used so far give out an intensive light coming from the filament of the bulb, which is visible from the space in front of the spotlight. Both interface between light and darkness and the uniformity of light beam intensity are difficult to obtain, the consequence of which is rather complicated systems. The big size of these lighting fittings and the slope of their cover glasses make suitable aerodynamic designing of the front part of the automobile to be a rather difficult task.
Spotlights used in stomatology have similarly low luminous efficiency. The light, coming from the light source, is directed to the front space and, therefore, stays unused. When the light is turned on, the light beam reaches also the patient's eyes and causes unpleasant dazzle. The dentist's mirror can also reflect unwanted light from different mirroring surfaces; thus the observed image can be disturbed. During some elemental operations, e.g. during preparation of the crown, the light, reflected from the metal, creates a certain kind of barrier between the preparation opening and the reflecting surface of the crown. This makes dental operation more difficult. The reflectors with raster mirrors are relatively big; when the lighting fitting is adjusted into an inapropriate position, the dentist can easily interrupt the light beam with his head and decrease the amount of light coming out from the lighting fittings and shining onto the desired spot on patient's body.
If another optical system, for example a system of condensors, is added to one of the systems mentioned and described above, the resulting system could be used for illumination of the object plane, in which a field of negative or positive filmstrip is inserted. Such field is then projected, by means of an objective, into the image plane. This lighting system is suitable mainly for projectors, slide projectors and enlarging apparatuses.
There are slide projectors of big formats with intensive light sources. Their structure and different luminance of the light source influence negatively the uniformity ratio of illumination of the object plane. Therefore, such lighting systems contain optical parts with raster members, and instead of a simple convex mirror, a raster mirror is used. Moreover, between two deflecting mirrors an intermediate image-forming system, consisting of two plates with raster lenses can be placed. For big format slides, a honeycombed condenser system, consisting of a raster lens, is mostly used. There are also used lighting systems made with one of the honeycombs as a raster mirror. The mirror consists of groups of curved reflecting raster surfaces, placed in one plane. The disadvantage of these systems is above all their big size and high number of complicated optical elements, what is the cause of bigger loss of the luminous flux as well.
In slide projectors of small formats are for illuminating systems used both spherical mirror with a light source and lens condenser system with an aspherical element and with a thermal filter. The disadvantage of such optical systems consists in the fact that the rectangular frame with film strip placed in the first principal plane, is illuminated by a light beam of a circular shape, which causes a loss of luminous flux. The angle of the luminous flux is furthermore limited by the marginal rays, caught by a spherical or aspherical condensor, and therefore this angle cannot be further increased.
In enlarging apparatuses, dedicated above all to amateurs, mostly the light sources for large areas are used, particularly opal lamps with a lens condenser system, or lamps with elliptic reflecting area. In some enlarging apparatuses can be used an independent head for a colour photography with its own light source, usually a halogen bulb with a diverging system, a mixing chamber for continuously adjustable colour filtration with an adjustable density diaphragm. Yet, such systems have very little light efficiency.